(a) Field of the Invention
The present invention relates to a liquid crystal display (written as LCD hereinafter), and more particularly, to an LCD of coplanar electrode mode (referred to as CE mode hereinafter) mode.
(b) Description of the Related Art
A CE mode LCD has a pair of panels, one of which has pluralities of pixel electrodes and common electrodes thereon. A plurality of liquid crystal molecules disposed between the two panels are driven by horizontal electric field generated by the pixel electrodes and the common electrodes, thereby obtaining wide viewing angle.
A plurality of pixel areas, being defined by the area enclosed by two adjacent gate lines and two adjacent data lines, are arranged in a matrix in a display area of a lower panel of a CE mode LCD. The pixel area has a switching element electrically connected to the gate lines and the data lines, a pixel electrode electrically connected to the switching element, and a common electrode cooperating with the pixel electrode to generate horizontal electric field. In a peripheral area, a plurality of gate pads connected to respective one ends of the gate lines, a plurality of data pads connected to respective one ends of the data lines, and a common electrode pad connecting the common electrodes of the pixel regions.
Color filters of red (R), green (G) and blue (B), and a black matrix between the color filters are formed on an upper panel of the CE mode LCD opposite to the pixel areas of the lower panel.
In the meantime, a panel test for inspecting circuital defects of the LCD is executed nearly before the completion of the manufacturing process. As a preparation for the panel test, during the manufacturing steps of the LCD, one ends of the gate lines are connected together, and a plurality of test pads are formed at the other ends of the gate lines.
In the panel test, two gate lines are selected and a test voltage is applied to the test pads of the selected gate lines to inspect defects of the pixels connected to the two gate lines. In this way, the panel test is executed on all the gate lines.
After the panel test of the LCD, all the gate lines are separated while the test pad are still remained.
The test pads connected to the gate lines are applied with gate voltages during the operation of the LCD. Since the gate off voltage (for example, −7 volts) is much different from the common voltage (for example, 5 volts) and the test pads have much larger width than the gate lines, the electric field from the test pads distorts the fields in the pixels adjacent to the test pads when the gate off voltage is applied to the test pad. In addition, the electric field from the test pads induces local polarization in the black matrix, which is very different from that due to the electric fields in the pixels, and thus significantly distorts the electric field in the pixels, thereby causing light-leakage.